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Logic Function Blocks Section 3-3
3-3-8 Reset Set Flip-Flop (RS-FF)
Basic Function When the input signal turns ON, RS-FF holds the ON status in the function
block and continuously connects to the output.
Diagram
General Description When the input condition to the Reset Set Flip-Flop function block is turned
ON, that ON status is maintained (latched) in the function block and the ON
output is maintained at the Output Enable signal.
The ON status is maintained in the function block, so the Output Enable signal
stays ON even if the input condition goes from ON to OFF.
The signal maintained in the function block is turned OFF when the function
block’s RESET condition is turned ON.
Fault Present Output
Setting
A Fault Present output can also be used in programming.
To enable this output, select the Fault Present check box on the Output Point
Tab Page of the function block properties dialog box.
Error Handling and
Error Resetting
Timing Chart
1. The Input signal turns ON, and so the Output Enable signal is turned ON.
2. The ON status is held, and so the Output Enable remains ON.
3. The Reset signal turns ON, and so the hold status is released.
4. The Input and Reset signals turn ON at the same time, and so the Fault
Present signal is turned ON.
Default Maximum Number of Outputs
Error condition Behavior for error detection Resetting the error
condition
Output Enable Fault Present
Input and Reset
are active simul-
taneously.
OFF
(safety state)
ON Make one of the signals
inactive.
Input
RESET
Fault Present
Output Enable
12 3 4
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